Response of carbon dioxide emissions to sheep grazing and N application in an alpine grassland – Part 1: Effect of sheep grazing

摘要

Previous work has failed to address fully the response of (autotrophic andheterotrophic) respiration to grazing in different ecosystems, particularlyin alpine grasslands outside the growing season. From 2010 to 2011 a fieldexperiment combined two methods (static closed chambers and a closed dynamicsoil CO₂ flux system) in alpine grasslands located in the TianshanMountains. We examined the effects of grazing regime on ecosystem respiration(R_e) both outside (NGS) and during (GS) the growing season anddetermined the pattern of R_e in relation to climate change. Therewas no significant change in CO₂ emissions under grazing. Heterotrophicrespiration (R_h) accounted for 78.5% of R_e withshort-term grazing exclusion and 93.2% of R_e with long-termgrazing exclusion. R_e, R_h and autotrophic respiration(R_a) fluxes outside the growing season were equivalent to12.9%, 14.1% and 11.4% of the respective CO₂ fluxesduring the growing season. In addition, our results indicate that soil watercontent played a critical role in R_a in the cold and aridenvironment. Both R_h and R_e were sensitive to soiltemperature. Moreover, our results suggest that grazing exerted nosignificant effect on CO₂ emissions in these alpine grasslands.